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An Introduction to Nishan

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Robot Hardware

Actuators:

Motors

Sensors:

Encoders

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Single pipeline bottleneck

This is an architecture only suitable for simple systems.

HardwareRobotBaseSoftware

publish publish

subscribe subscribe

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We will need an architecture which can suppmore complex hardware and softwarecomponents.

Goal: Develop big software for robots

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Challenges encountered in robotics

1. The world is asynchronous

2. Robots must manage significant complexity

3. Robot hardware requires abstraction

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Reusable code!

PR2 Roomba Care-O-bot 3

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MIT Urban Challenge Vehicle

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A meta-operating system forrobots

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What is ROS?

A Meta Operating System.

Open source

Runs in Linux (esp. Ubuntu)

Ongoing Windows implementation

Agent based (nodes)

Message passing

Publish Subscribe

Services via remote invocation

Supports numerous programming languages (C++, Python, L

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Comparison: the robotics ecosystem

Applications

Application building blocks

System software

Hardware

Applications

ROS

Hardware

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What is ROS

A meta operating system for robots

Open source

Runs in Linux (esp. Ubuntu)

Ongoing Windows implementation

Can be used with single-board computers like RPi, BBB, etc.

What is it NOT! : An actual operating system

A programming language

A programming environment / IDE

A hard real-time architecture

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What is ROS

Agent based system (nodes)

Message passing Publisher

Subscriber

Services via remote invocation

Supports numerous programming languages (C++, Python, L

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ROS: File system Level

ROS resources that are mainly encountered on disk:

Packages

Metapackages

Package Manifests

Message Types

Service Types

Source Code Files

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ROS Computation Graph Level

Peer-to-Peer network of ROS processes that are processing together

Nodes

Master

Parameter Server

Topics

Messages

Services Bags

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ROS : Community Level

ROS resources that enable separate communities to exchansoftware and knowledge.

Distributions

Repositories

ROS wiki

Mailing Lists

ROS Answers

Blog

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ROS & its main components

ROS Master

A centralized XML-RPC server

Negotiates communication connections

Registers and looks up names for ROS graph resources

Command roscore: starts master, parameter server, logging

Parameter Server

A shared, multi-variate dictionary that is accessible via network AP

Allows data to be stored by key

rosout

Essentially a network-based stdout for human-readable messages

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Package

A folder that contains your code, build files, launch files, etc

Can contain any number of nodes 'manifest.xml' lists the ROS & system dependencies

Should only contain related code

ex. laser pipeline, motor controllers, localization, SLAM, forwkinematics

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Nodes

Process that performs some function.

Communicate with each other using topics & services. Assigned unique names

Intended to be modular and operate on the fine-grained sca

Ex. For a package on motor controllers a node can be an actuator osensor.

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Ways to Communicate : Topics

Topic (publisher, subscriber)

Asynchronous "stream-like" communication Strongly-typed (ROS message specification)

Callback functions

By default single-threaded

Can be switched to multi-threaded implementation

Not appropriate for request/reply interaction

Many-to-many

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Publish/Subscribe Messaging

Publish: Will not block until receipt, messages get queued.

Delivery Guarantees: Specify a queue size for publishers: If publishing towill buffer a maximum of X messages before throwing away old ones

Transport Mechanism: TCP/IP

Master

Publisher

Publisher

Subscriber

Subscriber

/topic

(DNS-like)

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Ways to communicate : Service

Higher Priority

Synchronous "function-call-like" communication Strongly-typed (ROS service specification)

One-to-one

Can have one or more clients

No topic callbacks are issued during service call

Service request is blocking

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ROS Tools

PlottingGraph Visualization

Diagnostics

Simulation/visualization

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ROS debugging tools

rostopic: Display debug information about ROS topics: publisubscribers, publishing rate, and message content.

rostopic echo [topic name] prints messages to console

rostopic list prints active topics

rqtplot : Plot data from one or more ROS topic fields using m

rqtplot /turtle1/pose/x,/turtle1/pose/y graph data from 2 top

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ROS Visualization

Visualize:

Sensor data

Robot joint states

Coordinate frames

Maps being built

Debugging 3D markers

Visualization/Simulation Tools

RVIZ

Gazebo

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ROS: Over Network

Two ways to connect different machines in a Network

Exporting ros master to a single machine

Different machines can use just one instance of roscore

Using Multimaster replication

Different roscore instances synchronize with each other

Already implemented in ROS package Multimaster_fkie

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ROS Resources

http://www.ros.org

http://wiki.ros.org

http://www.ros.org/http://www.ros.org/http://wiki.ros.org/http://wiki.ros.org/http://wiki.ros.org/http://www.ros.org/

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Thank you!